Automatic weight application machine

ABSTRACT

A machine is provided for automatically applying a balance correcting weight (44)-and-clip (46) assembly to a vehicle wheel-and-tire assembly (12). The machine includes a conveyor (20) portion for conveying the wheel-and-tire assembly (12) to which the balance-correcting weight (44) is to be applied to a weight (44) application station, orienting the wheel-and-tire assembly (12) properly to receive at the correct location the balance-correcting weight (44), and conveying the wheel-and-tire assembly (12) to which the balance-correcting weight (44) has been applied away from the weight (44) application station. The machine includes a hammer (22, 24) having a storage orientation permitting conveying of the wheel-and-tire assembly (12) to and from the weight (44) application station and a use orientation adjacent the wheel-and-tire assembly (12) to which balance correcting weight (44) is to be applied, and means for moving the hammer (22, 24) selectively between its storage and use orientations to permit conveying of the wheel-and-tire assembly (12) to the weight (44) application station, application of the balance-correcting weight (44) to the wheel-and-tire assembly (12), and conveying of the wheel-and-tire assembly (12) to which a balance correcting weight (44) has been attached away from the weight (44) application station. The hammer (22, 24) includes a jaw (40) with a contour conforming to the shape of the clip (46) and a shank (50) portion. The shank (50) portion and jaw (40) comprise ferromagnetic material. An electrically conductive coil (94) surrounds the shank (50) portion of the hammer (22, 24). The hammer (22, 24) is driven through operating cycles to hammer (22, 24) the weight (44)-and-clip (46) assembly onto the wheel.

This is a continuation of U.S. patent application Ser. No. 07/039,586filed Apr. 16, 1987 (now abandoned).

This invention relates to automatic weight application machines forapplying correcting weights to rotary elements once the amounts andlocations of weight required to correct imbalance existing in suchrotary elements are determined. The invention is disclosed in thecontext of a machine for automatically applying balance correctingweights to vehicle wheel-and-tire assemblies. However it is believedthat the invention is useful in other applications in which balancecorrecting weights are to be applied to other types of rotary elementsas well.

American style single component balance correcting weights includeselected different mass value portions, typically of lead, with amolded-in-place, spring steel clip to retain the lead mass on the wheelrim flange. Customarily, these balance-correcting weights have beenmanually selected, positioned on the flange at the point wherecorrection is to be applied, and installed by driving the clip portiononto the flange with a hammer.

Techniques and apparatus for applying balance correcting weights tovehicle wheel-and-tire assemblies are known. For example, U.S. Pat. No.3,623,208 describes a machine which utilizes the European-style two-partweight-and-clip correction scheme. In this machine, the tire istemporarily pressed away from the wheel flange. The retaining clip isslipped into place over a dummy weight form. The tire is then released.The dummy weight form is removed and the clip is held in place,sandwiched between the wheel flange and the tire. The proper correctionweight is then inserted under the clip to complete the balancecorrection process. The mechanism of U.S. Pat. No. 3,623,208 onlyachieves the installation of the retaining clip. The actual correctingweight is manually inserted later.

In U.S. Pat. No. 4,554,734 a means for handling the European-styleweights is described along with a simplified installation technique inwhich the temporary use of the dummy weight form is not necessary. Theactual balance-correcting weight is placed on the wheel and theretaining clip is then pushed onto the wheel rim flange by anothermechanism, avoiding the need to press the tire away from the wheelflange. The mechanism of U.S. Pat. No. 4,554,734 achieves the completeinstallation of the European two-piece correction weights, but would notaccommodate the American-style weights due to their changing andirregular shapes.

In German Patent Specification No. 941,956, a mechanism is described toinstall an American-style one piece correction weight with a molded-inretaining clip. This mechanism retains the weight in a pressure pad witha spring and pushes the assembly onto the wheel flange using a C-clamparrangement manually actuated through a mechanical linkage. Themechanism of German Patent Specification No. 941,956 employs aform-fitting pressure pad and spring retainer to install theAmerican-style one-piece weight-and-clip-assembly manually, but makes noprovision for handling the weight and would be difficult to automate.

It is an object of the present invention to provide an apparatus whichis readily adaptable to a system for automatically applyingAmerican-style, single component, balance-correcting weights to vehiclewheel-and-tire assemblies.

The present invention eliminates the need to depress the sidewall of thetire away from the wheel rim, provides a mechanism by whichirregularly-shaped, American-style weights can be manipulated by theircommon features, and transported to an application station in the properorientation for application, and provides a mechanism by which theweights can be installed automatically.

According to the present invention, preparation for the application of abalance-correcting weight-and-clip assembly to a vehicle wheel-and-tireassembly comprises conveying the wheel-and-tire assembly into a knownposition in the application machine, orienting the location on thewheel-and-tire assembly to which balance-correcting weight is to beapplied in a known position, and bringing the balance-correctingweight-and-clip assembly into a closely spaced relation adjacent to thelocation on the wheel-and-tire assembly to which the correcting weightis to be applied.

According to one aspect of the invention, a method for automaticallyapplying a balance correcting weight including a ferromagnetic portionto a rotary element comprises orienting the weight for application byplacing a magnet on the weight in close proximity to the ferromagneticportion, conveying the magnet into close proximity to the rotaryelement, relatively orienting the rotary element and magnet so that theweight carried by the magnet is properly oriented to be applied to therotary element to correct imbalance existing in the rotary element, andmoving the magnet to apply the weight to the rotary element.

Additionally, according to this aspect of the invention, the rotaryelement comprises a vehicle wheel-and-tire assembly, the weightcomprises a weight-and-clip assembly including a clip for mounting theweight on a flange of the vehicle wheel-and-tire assembly, and the stepof moving the magnet to apply the weight to the rotary element comprisesthe step of rapidly reciprocating the magnet relative to the flange ofthe vehicle wheel-and-tire assembly to which the weight is to be appliedto hammer the clip onto the flange.

Further according to this aspect of the invention, the step ofrelatively orienting the rotary element and magnet so that the weightcarried by the magnet is properly oriented to be applied to the rotaryelement to correct imbalance existing in the rotary element comprisesthe steps of relatively conveying the rotary element and magnet with thelocation on the rotary element to which balance correcting weight is tobe applied in known orientation, and bringing the magnet into closelyspaced relation adjacent to the location on the rotary element to whichbalance correcting weight is to be applied.

According to this aspect of the invention, the step of orienting theweight for application by placing a magnet on the weight in closeproximity to the ferromagnetic portion comprises the steps of providingan electromagnet including an electromagnetic coil and a ferromagneticportion, orienting the electromagnet with the ferromagnetic portion ofthe electromagnet adjacent the weight to be applied, and passing anelectrical current through the electromagnetic coil to attract theferromagnetic portion of the weight into close proximity to theferromagnetic portion of the electromagnet.

Additionally, according to this aspect of the invention, the methodfurther comprises the step of interrupting the current through theelectromagnetic coil.

According to another aspect of the invention, apparatus forautomatically applying a balance correcting weight including aferromagnetic portion to a rotary element comprises means for orientingthe weight for application by placing a magnet on the weight in closeproximity to the ferromagnetic portion, means for conveying the magnetinto close proximity to the rotary element, means for relativelyorienting the rotary element and magnet so that the weight carried bythe magnet is properly oriented to be applied to the rotary element tocorrect imbalance existing in the rotary element, and means for movingthe magnet to apply the weight to the rotary element.

Additionally, according to this aspect of the invention, the rotaryelement comprises a vehicle wheel-and-tire assembly, the weightcomprises a weight-and-clip assembly including a clip for mounting theweight on a flange of the vehicle wheel-and-tire assembly, and the meansfor moving the magnet to apply the weight to the rotary elementcomprises means for rapidly reciprocating the magnet relative to theflange of the vehicle wheel-and-tire assembly to which the weight is tobe applied to hammer the clip onto the flange.

Further according to this aspect of the invention, the means forrelatively orienting the rotary element and magnet so that the weightcarried by the magnet is properly oriented to be applied to the rotaryelement to correct imbalance existing in the rotary element comprisesmeans for rotating the location on the rotary element to whichbalance-correcting weight is to be applied into known orientation, andmeans for bringing the magnet into closely spaced relation adjacent thelocation on the rotary element to which balance correcting weight is tobe applied.

Further according to this aspect of the invention, the means fororienting the weight for application by placing a magnet on the weightin close proximity to the ferromagnetic portion comprises means forproviding an electromagnet including an electromagnetic coil and aferromagnetic portion, means for orienting the electromagnet with theferromagnetic portion of the electromagnet adjacent the weight to beapplied, and means for passing an electrical current through theelectromagnetic coil to attract the ferromagnetic portion of the weightinto close proximity to the ferromagnetic portion of the electromagnet.

According to this aspect of the invention, means are provided forinterrupting the current through the electromagnetic coil.

The invention may best be understood by referring to the followingdescription and accompanying drawing which illustrate the invention. Inthe drawings:

FIG. 1a illustrates an entry-side elevational view of a station to whichwheel-and-tire assemblies requiring the addition of balance correctingweights are conveyed, where balance correcting weights are automaticallyapplied to the upwardly facing rim flanges of the wheel-and-tireassemblies, and away from which the wheel-and-tire assemblies areconveyed after the application of balance correcting weights;

FIG. 1b illustrates an entry-side elevational view of a station to whichwheel-and-tire assemblies requiring the addition of balance correctingweights are conveyed, where balance correcting weights are automaticallyapplied to the downwardly facing rim flanges of the wheel-and-tireassemblies, and away from which the wheel-and-tire assemblies areconveyed after the application of the balance correcting weights;

FIG. 2 illustrates a fragmentary side elevational view of certaindetails of the station illustrated in FIGS. 1a-b;

FIG. 3 illustrates a perspective view of certain of the detailsillustrated in FIG. 2;

FIG. 4 illustrates a fragmentary side elevational view of certaindetails of the stations illustrated in FIGS. 1a-b;

FIG. 5 illustrates an exploded perspective view of the detailsillustrated in FIG. 4; and

FIG. 6 illustrates a fragmentary side elevational view of certaindetails of the stations illustrated in FIGS. 1a-b;

Turning to FIG. 1a, an automatic weight application station 10 forapplying balance correcting weights to wheel-and-tire assemblies 12 isviewed from its entry end 14. Station 10 includes a framework 16 forsupporting the station's operating mechanisms which include a chuck 18and a conveyor/elevator mechanism 20, both of known construction, andtwo automatic weight application hammers 22, 24. Hammer 22 is mountedabove and to one side of chuck 18. Hammer 24 is mounted above and to theother side of chuck 18. Hammers 22, 24 are mounted on carriages 26, 28,respectively, for movement between non-use orientations, illustrated bythe solid-line position of hammer 22 and the broken-line position ofhammer 24, and use orientations, illustrated by the broken-line positionof hammer 22 and the solid-line position of hammer 24. Carriages 26, 28include means such as, for example, rodless pneumatic cylinders, toreciprocate hammers 22, 24 between their use and non-use orientationsunder the control of, for example, a programmable controller.

The non-use orientations of hammers 22, 24 permit wheel-and-tireassemblies 12 requiring balance correction to be conveyed on a conveyorsection 20 into the station 10. Conveyor section 20 is then lowered,depositing the wheel-and-tire assemblies requiring correction onto chuck18. Since the amount(s) and location(s) of correctable imbalance(s) inthe wheel-and-tire assemblies 12 have already been determined and theorientations of the wheel-and-tire assemblies are known, the chuckmechanism 18 can be driven rotatably to orient the location(s) ofimbalance of the wheel-and-tire assemblies beneath the use (broken-line)orientation of hammer 22 or below the use (solid-line) orientation ofhammer 24, depending upon whether the wheel of the particularwheel-and-tire assembly, the imbalance of which is being corrected, issteel or aluminum. If the wheel is steel, hammer 22 is used. If thewheel is aluminum, hammer 24 is used. Once the balance correcting weighthas been applied, carriages 26, 28 return to their non-use orientations,chuck mechanism 18 releases the wheel-and-tire assembly, theconveyor/elevator section 20 elevates the wheel and tire assembly offthe chuck mechanism 18, raising the assembly 12 back to the broken lineorientation illustrated in FIG. 1a, and the wheel-and-tire assembly isconveyed out of station 10 for further processing via an overheadtransfer mechanism 19.

It is to be understood that the balance correction system here describedis a two plane system, and that a companion station 10' illustrated inFIG. 1b is located immediately upstream or downstream from station 10.This companion station has a hammer 24' in the oblique orientation ofhammer 24 but below a chuck 18', for application of balance correctionweights to the lower flanges of horizontally oriented aluminum wheels.By the same token, this companion station 10' has a hammer 22' in thevertical orientation of hammer 22 but below chuck 18', for applicationof balance correcting weights to the lower flanges of horizontallyoriented steel wheels. The vertically oriented hammers 22, 22' are usedin the application of balance correcting weights to steel wheels. Theobliquely oriented hammers 24, 24' are used in the application ofbalance correcting weights to aluminum wheels.

Closer consideration of the construction of hammers 22, 22' is permittedwith reference to FIGS. 2-5. Hammer 22 is illustrative. It includes ajaw portion 40 having a contour 42 conforming, at least in part, to thetransverse sectional shape of a portion of a combination balancecorrecting weight 44 and clip 46 for correcting imbalance in a steelwheel. Clip 46 is constructed from a ferromagnetic material, such asspring steel. Weight 44 typically is lead or a lead alloy molded ontoclip 46. Hammer 22 also includes a shank portion 50 joined to jawportion 40 at a somewhat rectangular pad 52 integrally formed with shank50, FIGS. 4-5. A center section 54 of jaw portion 40 is also integrallyformed with shank 50. Center section 54 extends generally transverselyto the longitudinal extent of shank 50 and also transversely to theradii of wheel and tire assemblies onto which hammer 22 hammers balancecorrecting weights. The surface 56 of center section 54 remote from pad52 provides a portion of the contour 42. Bevelled surfaces 58, 60 ofcenter section 54 are provided adjacent surface 56. Shank portion 50,pad 52 and center section 54 are machined from a ferromagnetic materialsuch as mild steel.

Side surfaces 62, 64 (FIG. 5) of jaw 40 are provided by inserts 66, 68,respectively. Side surfaces 62, 64 provide part of the contour 42.Inserts 66, 68 are also provided with surfaces 70, 72, 74 and 76, 78, 80which abut pad 52 and center section 54. Inserts 66, 68 are constructedfrom non-magnetic material. Illustratively, inserts 66, 68 areconstructed from stainless steel and are attached to pad 52 and centersection 54 by brazing.

Shank 50 is provided near its upper end with a through passageway 82.Another opening 84 is provided in shank 50 between passageway 82 and pad52.

Hammer 22 also includes a bobbin 86 which illustratively is molded fromnylon. Bobbin 86 includes a column 88 providing a central passageway 89which slidably receives shank 50, an endplate 90, a socket 92 forreceiving an electrical connector (not shown) by which electricalcontact can be made from a current source (not shown) in station 10 to acoil 94 (illustrated in broken lines) of several turns of insulated wirewound on bobbin 86, a square cross-section portion 96, and an endplate98. Square cross-section portion 96 is received in a square slot oncarriage 26 to prevent bobbin 86 from turning relative to carriage 26.Central passageway 89 includes a longitudinally extending, generallyrectangular cross-section slideway 100 (FIG. 3) which receives a locatorpin 102 with which opening 84 is fitted. The engagement of locator pin102 in slideway 100 prevents rotation of shank 50 in passageway 89.Endplate 90 cooperates with pad 52 to retain shank 50 in bobbin 86 inone direction. A key 104 insertable through passageway 82 cooperateswith endplate 98 to retain shank 50 in bobbin 86 in the other direction.

An air hammer 110 (FIG. 1) is associated with carriage 26. Air hammer110 receives the end 112 (FIGS. 4-5) of shank 50 remote from jaw 40.Actuation of air hammer 110 drives the hammer 22 through cycles ofoperation to drive a weight 44 and clip 46 assembly onto the flange of asteel wheel rim. Air hammer 110 illustratively is an Ingersoll-RandModel AVC13-C1 suitably valved to operate hammer 22 under the control ofa process controller.

Referring to FIG. 6, hammers 24, 24' are similarly configured to hammers22, 22' except that the contour 142 of hammers 24, 24' conforms, atleast in part, to the transverse sectional shape of a portion of acombination balance correcting weight 144 and clip 146 for correctingimbalance in an aluminum wheel.

In operation, a means (not shown) for delivering a balance correctingweight in the proper orientation to be engaged by hammer 22 or 24conveys the appropriate weight to the hammer while the hammer is in itsnon-use orientation. Such a delivery means can comprise multiplevibratory feeders with a programmable controller operated gate forselecting which feeder is to supply balance correcting weight to correctimbalance in a particular wheel and tire assembly 12. For example, iffive different weights, illustratively, 0.5 oz., 1.0 oz., 1.5 oz., 2.0oz. and 2.5 oz. (14 g., 28 g., 42.5 g., 56.7 g. and 70.9 g.,respectively) are available to correct imbalance in vehicle wheel andtire assemblies passing along conveyor 20, five vibratory feeders feedweights for correcting imbalances in steel wheels to the non-useposition of hammer 22. Five vibratory feeders feed weights forcorrecting imbalances in aluminum wheels to the non-use position ofhammer 24. The feeders feed weights in the proper orientations to theirrespective jaws 40, 140.

As the appropriate weight to correct an imbalance in a plane of aparticular steel or aluminum wheel and tire assembly 12 is presented atthe appropriate jaw 40, 140, the coil 94 associated with that jaw 40,140 is energized to capture the appropriate weight 44, 144 and clip 46,146 assembly in the jaw 40, 140. Concurrently, the conveyor section islowered to lower the wheel and tire assembly 12, the imbalance of whichis to be corrected, onto the chuck 18. The chuck 18 orients theunbalanced wheel-and-tire assembly with the location at which weight isto be applied under the use position of hammer 22 (for steel wheels) orhammer 24 (for aluminum wheels). The hammer 22 or 24 is then advanceduntil the weight-and-clip assembly comes to rest in contact with thewheel flange at the location at which the correcting weight-and-clipassembly is to be applied. The pneumatic hammer 110 associated with theappropriate hammer 22, 24 is then driven to execute a number ofoperating cycles to hammer the appropriate weight onto thewheel-and-tire assembly at the appropriate location. The coil 94 is thendeenergized to release the weight-and-clip assembly. The carriage 26, 28is then retracted to its non-use orientation. The conveyor is elevated,and the wheel-and-tire assembly, with balance-correcting weightattached, proceeds to further processing.

What is claimed is:
 1. A method for automatically applying a balancecorrecting weight-and-clip assembly to a vehicle wheel-and-tireassembly, the method comprising the steps of: providing aweight-and-clip assembly including a ferromagnetic clip to which abalance-correcting weight is attached; conveying a wheel-and-tireassembly to which the balance-correcting weight is to be applied to aweight application station; orienting the wheel-and-tire assemblyproperly to receive at the correct location the balance-correctingweight; moving a hammer from a storage orientation out of operatingposition permitting conveying of the wheel-and-tire assembly to and fromthe weight application station and then to a use orientation inoperating position adjacent the wheel-and-tire assembly to which balancecorrecting weight is to be applied, the hammer comprising a jaw having acontour conforming to the shape of the clip, a shank portion, the shankportion and the jaw being provided with ferromagnetic material, and anelectrically conductive coil surrounding the shank portion; energizingthe coil, thereby capturing the weight and clip assembly in the jaw;then driving the hammer through operating cycles, thereby hammering theweight and clip assembly onto the wheel and tire assembly; and thenconveying the wheel-and-tire assembly to which a balance correctingweight has been applied away from the weight application station.
 2. Themethod of claim 1 further comprising movably mounting the hammerrelative to the coil to permit driving of the hammer through operatingcycles without requiring corresponding movement of the coil.
 3. Themethod of claim 2 wherein movably mounting the hammer relative to thecoil includes providing a passageway through the coil, sizing the shankof the hammer for sliding insertion into the passageway, and retainingthe shank in the passageway.
 4. The method of claim 1 wherein providingthe shank portion and jaw with ferromagnetic material comprisesconstructing a portion of the jaw from ferromagnetic material to contactthe ferromagnetic clip to manipulate the weight-and-clip assembly whencurrent is passed through the coil and constructing a portion of the jawfrom a non-magnetic, relatively harder material than the ferromagneticmaterial to provide a surface for hammering the weight onto the wheel.5. The method of claim 4 wherein constructing a portion of the hammerfrom ferromagnetic material includes constructing the portion of the jawof the hammer from mild steel and constructing a portion of the jaw froma non-magnetic, relatively harder material comprises constructing aportion of the jaw from stainless steel.
 6. The method of claim 4wherein constructing a portion of the jaw from ferromagnetic materialcomprises constructing a central spine of the jaw which extendsgenerally transversely to the shank portion and generally transverselyto the radius of a wheel-and-tire assembly at the point at which thebalance correcting weight is to be applied from ferromagnetic material,and constructing a portion of the jaw from a non-magnetic, relativelyharder material comprises constructing first and second hammeringsurface-providing portions from a non-magnetic, relatively hardermaterial, and locating one of the hammering surface-providing portionson one side of the spine and the other of the hammeringsurface-providing portions on the other side of the spine.
 7. The methodof claim 6 wherein constructing the spine from ferromagnetic materialcomprises constructing the spine from mild steel and constructing thehammering surface providing portions from a non-magnetic, relativelyharder material comprises constructing the hammering surface-providingportions from stainless steel.
 8. A machine for automatically applying abalance correcting weight (44)-and-clip (46) assembly to a vehiclewheel-and-tire assembly (12), the weight (44)-and-clip (46) assemblyincluding a ferromagnetic clip (46) to which a balance-correcting weight(44) is attached, the machine including a conveyor (20) portion forconveying the wheel-and-tire assembly (12) to which thebalance-correcting weight (44) is to be applied to a weight applicationstation, orienting the wheel-and-tire assembly (12) properly to receiveat the correct location the balance-correcting weight (44), andconveying the wheel-and-tire assembly (12) to which thebalance-correcting weight (44) has been applied away from the weightapplication station, the machine further including a hammer (22, 24)having a storage orientation out of operating position permittingconveying of the wheel-and-tire assembly (12) to and from the weightapplication station and a use orientation in operating position adjacentthe wheel-and-tire assembly (12) to which balance correcting weight (44)is to be applied, and means (26, 28) for moving the hammer (22, 24)selectively between its storage and use orientations to permit conveyingof the wheel and tire assembly (12) to the weight application station,application of the balance-correcting weight (44) to the wheel-and-tireassembly (12), and conveying of the wheel-and-tire assembly (12) towhich a balance correcting weight (44) has been attached away from theweight application station, the hammer (22, 24) including a jaw (40)with a contour (42) conforming to the shape of the clip (46) and a shankportion (50), the shank portion (50) and jaw (40) comprisingferromagnetic material, an electrically conductive coil (94) surroundingthe shank portion (50) of the hammer (22, 24), and means (110) fordriving the hammer through operating cycles to hammer theweight-and-clip assembly onto the wheel.
 9. The machine of claim 8further comprising means (84, 86, 88, 89, 100, 102) for movably mountingthe hammer (22, 24) relative to the coil (94) to permit driving of thehammer (22, 24) through operating cycles without requiring correspondingmovement of the coil (94).
 10. The machine of claim 9 wherein the means(84, 86, 88, 89, 100, 102) for movably mounting the hammer (22, 24)relative to the coil (94) includes means (86, 89) providing a passageway(89) through the coil (94), the shank (50) of the hammer (22, 24) sizedfor sliding insertion into the passageway (89), means (52, 90, 98, 104)for retaining the shank (50) in the passageway (89), and means (96) formounting the coil (94) on the machine.
 11. The apparatus of claim 8wherein the jaw (40) of the hammer (22, 24) includes a portion (54)constructed from ferromagnetic material to contact the ferromagneticclip (46) to manipulate the weight (44) -and-clip (46) assembly whencurrent is passed through the coil (94) and a portion (66, 68)constructed from a non-magnetic, relatively harder material than theferromagnetic material to provide a surface (62, 64) for hammering theweight (44) onto the wheel.
 12. The apparatus of claim 11 wherein theportion (54) of the hammer (50) which is constructed from ferromagneticmaterial is constructed from mild steel and the non-magnetic, relativelyharder material (66, 68) comprises stainless steel.
 13. The apparatus ofclaim 11 wherein the portion (54) of the jaw (40) which is constructedfrom ferromagnetic material comprises a central spine (54) which extendsgenerally transversely to the shank portion (50) and generallytransversely to the radius of a wheel-and-tire assembly (12) at thepoint at which the balance correcting weight (44) is to be applied, andthe portion (66, 68) of the jaw which is constructed of a non-magnetic,relatively harder material comprises first (66) and second (68)hammering surface-providing portions, one (66) of the hammeringsurface-providing portions located on one side of the spine (54) and theother (68) of the hammering surface-providing portions located on theother side of the spine (54).
 14. The apparatus of claim 13 wherein thespine (54) is constructed from mild steel and the hammeringsurface-providing portions (66, 68) are constructed from stainlesssteel.